This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The purpose of this study is to conduct a longitudinal multidisciplinary investigation of the natural history, morbidity, and mortality in people with Urea Cycle Disorders (UCD). The total number of subjects will be 200. Approximately 30 participants will be enrolled per year. Age can range from 1day to 99 years. The duration of the study will be 20 years.